1. Field of the Invention
The present invention relates to a map data storage medium (database) for storing map data divided into a plurality of meshes, and to a map information retrieving apparatus or a navigation apparatus utilizing the medium.
2. Description of the Related Art
The number of vehicles provided with on-vehicle navigation apparatuses for route guidance is increasing. Such a navigation apparatus is typically equipped with a map database carried on a storage medium such as a DVD, identifies a current position detected by a GPS (global positioning system) apparatus or the like as a position on the map, and displays the position. When a destination is set, an optimum route from the current position to the destination is searched for. More specifically, with data on road network contained in the map database, the shortest distance between the present position and the destination is searched for using linear programming to retrieve the optimum route. In addition to the distance, a route requiring the shortest time can be obtained by using stored data on speed at which the vehicle travels on the road. The map database also contains data on facilities of various types, and therefore, by entering a facility to be searched for, such as a department store, a convenience store, a train station, or a hospital, information on such facilities located around the current position can be retrieved.
For arranging and storing map data in the map database, the map is divided into a plurality of meshes as a matrix, and a mesh number is assigned to each of the meshes. The meshes are classified into primary meshes, secondary meshes, and so on. The map is roughly divided into primary meshes, which are further divided into secondary meshes, which are further subdivided into tertiary meshes. By thus dividing the map data into meshes for storage and allocating a mesh number to each mesh, map data for an area corresponding to a designated mesh number can be obtained.
However, mesh numbers are conventionally assigned according to how they are arranged in the matrix. As a result, it is often the case that neighboring meshes are not necessarily assigned with contiguous numbers. More specifically, while the problem is not so significant for primary meshes because the division is quite rough, secondary meshes located adjacent to each other are often assigned with quite distant numbers because the numbers are assigned according to how they are arranged in the primary mesh.
Further, map data for a relatively wide area must be searched for in order to obtain information on a facility. In such a case, the time required for the search increases when the map data portions to be retrieved are allocated with distant mesh numbers. In addition, when the world map is concerned, mesh allocation methods are not standardized, requiring separate systems be created for respective areas and data on the manner of allocating the meshes be provided.
The present invention has been conceived in view of the above problems, and aims to provide a map database allowing efficient number assignment.
A map data storage medium (database) according to the present invention stores map data divided into a plurality of meshes. Starting from a base mesh, a prescribed number of meshes located in close proximity are sequentially assigned with numbers following an order determined by a prescribed rule. The assignment process is repeated using another mesh as the base mesh. By thus assigning numbers to respective meshes, sorted map data is stored in accordance with the assigned numbers.
Thus, adjacent meshes are numbered in accordance with a prescribed rule, and the map data portions are stored in numerical order, whereby data portions for the meshes adjacent on the map are located in close proximity on the storage medium. Because the map database is often used to search a relatively wide area and data portions are located in close proximity on the storage medium, efficiency in accessing the storage medium for a search is improved.
Preferably, after numbers are assigned to the prescribed number of meshes as described above, the meshes having the assigned numbers are collected as one large mesh. Further, the number assignment process is then applied to other large meshes following the order determined by the above prescribed rule. For the meshes included in each of the large meshes, numbers are sequentially assigned to adjacent meshes following the order determined by the above prescribed rule. A prescribed number of the large meshes are further collected to form an even larger mesh. The number assignment process is then applied to such larger meshes following the order determined by the above prescribed rule, and numbers are assigned to each mesh in these larger meshes. By repeating the above-described process, numbers are assigned to the entire map.
The above-described process makes it possible to assign numbers worldwide according to a prescribed rule, and to build a systematic map database.
Preferably, the above prescribed rule includes a basic rule in which numbers are assigned to four meshes following an N pattern, starting from a base mesh and proceeding to a mesh above the base, a mesh on the right thereof, and then a mesh on the upper right thereof. Such rule is relatively simple, and also allows numbers to be sequentially assigned to meshes located in close proximity.
The map data preferably includes a building ID for identifying a building. The building ID is used to identify a building and facilitate a search for facilities in the same building. The map data for display only contains the building ID and the detailed data can be stored in different space and accessed using the building ID, to thereby enhance speed of scrolling the displayed map.
Preferably, a plurality of meshes are collected to form an integrated mesh, and the above mesh number includes an integrated mesh number which is a mesh number for one of the plurality of meshes forming the integrated mesh. By thus forming an integrated mesh, map data can be retrieved collectively, leading to efficient access.
The map information retrieving apparatus according to the present invention is characterized in that the above-described map data storage medium is used to retrieve map information.
The navigation apparatus according to the present invention is characterized in that the above-described map data storage medium is used for route guidance.